A bore hole or well bore is an artificially prepared hole, typically drilled into the ground with heavy duty drilling equipment in order to tap and extract underground water, oil, gas and other resources. Exploratory holes may also be drilled to locate mineral deposits, ground water, geothermal supplies and even to determine pollution levels at various depths in the ground.
It has long been known in the art that the visual examination of the strata forming the walls of a bore hole may be of significant value to a trained geologist. Such a visual examination may also be valuable in maintaining and repairing an operational bore hole. For example, after a steel casing has been in place in a bore hole for some time, rusting damage or shifts in the earth may cause rupturing or uncoupling of the steel casing. In such an instance, a visual examination of the casing shows the extent of the damage as well as the feasibility of repairs.
Further, in certain instances equipment may become lodged or stuck in the bore hole. This may result, for example, from either cave-ins or sedimentation during operation of the equipment. In such an instance, a camera may be lowered into the bore hole to locate the point of the cave-in and/or the lodged equipment and thereby determine the feasibility and approach for a recovery operation.
In order to achieve this end, a number of down hole camera apparatus, including video camera apparatus, have been developed. An example of one such apparatus is disclosed in U.S. Pat. No. 4,855,020 to Barbour. The Barbour patent discloses a down hole video camera apparatus wherein the video camera is held in the first section of a protective tubular housing. The video camera is equipped with a wide-angle lens to allow viewing of the wall of the bore hole. A lighthead assembly including a light source is attached to the housing. This light source illuminates the wall of the bore hole so as to allow videotaping in the bore hole as the camera assembly is lowered downwardly by means of a cable.
While down hole camera apparatus of the type disclosed in Barbour provide effective visual logging of bore holes, such prior art camera apparatus suffer a number of drawbacks that limit their application and usefulness. More particularly, such prior art camera apparatus incorporate conventional optic systems. These fail to provide sufficient thermal protection to the imaging section of the camera. In fact, the design of many prior art optic systems actually serves to direct or funnel the heat from the environment to the imaging section.
As temperatures of well over 300.degree. F. are often encountered in deep bore holes, heat is quickly transferred. The resulting increase in temperature eventually reaches a level which causes the imaging section to cease operating. Hence, prior art down hole camera apparatus provide effective operation for only a limited period of time. In many instances the operational period is not sufficiently long to allow completion of the task at hand such as the viewing of a fishing operation. Accordingly, the camera must be brought up from the bore hole and cooled to an operating temperature or replaced with another camera before work may be completed. This is a time consuming and, therefore, expensive operation. Thus, a need is identified for a solution to this problem.